This invention relates to telephone terminal bases.
Many designs of telephone terminals are intended to be used in environmental conditions which may deleteriously affect operating equipment within the terminal if the equipment is brought into contact with corrosive elements in the environment. Such telephone terminal designs include those which are to be used as public telephone terminals in damp and/or corrosive atmospheric conditions which may, for instance, damage on-off conductive contacts within the terminal, thereby rendering the terminal unusable.
Conventionally, dialing is now accomplished by selectively pressing dialing buttons of a set which slideably protrude from a front of a public telephone terminal, and depressing any button applies a bridging conductor across a pair of spaced contacts on a printed circuit board for passage of a dialing signal. In an attempt to prevent surfaces of the bridging conductor of the spaced contacts from damp corrosive atmospheric damage, it is known to dispose a barrier layer between the button set and the printed circuit board. The barrier layer has a resiliently deflectable region between each button and its corresponding printed circuit board contacts and which is resiliently deflected towards the contacts each time the button is depressed. Each resiliently deflectable region has a bridging conductor disposed on one side of it and which is caused to bridge the corresponding contacts upon depression of its button so that a dialing circuit is completed to produce a dialing signal.
Unfortunately, screw-threaded means are required to hold together a front of the terminal base, the barrier layer, and the printed circuit board, and it has been found that corrosive elements from the ambient atmosphere have been bypassing barrier layers by passage along the screw threads from one side of the barrier layers to the other, and ultimately the electronic and electrical contact parts do become damaged.